When car tires contact a road surface, they generate considerable noise. At speeds above 25 mph in certain vehicles, tire noise can be greater than all other sources of automotive noise combined. Accordingly, car and tire manufacturers spend large amounts of resources every year on research and development to reduce tire noise.
Tire noise results from many sources. For example, tire noise results from (1) low-frequency shock waves produced by excitation of the internal tire air chamber from tire deformation caused by the contact of the tire with the road surface; (2) low-frequency tire structure ringing due to air chamber excitation caused by the deflection of the tire at road contact; (3) high-frequency external tread air compression caused by air temporarily trapped between the tread and the road surface; and (4) high-frequency contact scrub caused by the friction between the tire and the road surface.
Some tread air compression noise is not avoidable. For example, tread air compression acts to clear water from the tread contact surface by compressing the water and air at road contact and then expanding the mixture at tread release. Additionally, some contact scrub noise is not avoidable because tires have finite adhesion which generates friction and noise with the road surface.
Shock wave energy from tire deformation is transmitted from the tread contact area into the internal tire air chamber created by the tire and the wheel upon which the tire is mounted. The energy transmitted into the internal tire air chamber is only dissipated by tire ringing and coupling of the noise to the wheel. Such tire ringing and noise coupling comprise a large portion of the total amount of tire noise.
Conventional methods for reducing tire noise have several deficiencies. In particular, those methods do not effectively absorb low-frequency energy (e.g., below 800 Hz) associated with the shock waves that produce tire noise. As tires generate significant low-frequency energy, an efficient tire noise absorber should reduce the noise produced by such low-frequency energy. However, conventional methods do not adequately reduce that noise. Additionally, low-frequency noise increases perceived high frequency noise produced by tread air compression and tire scrub. Accordingly, conventional methods fail to reduce the perceived high frequency tire noise by failing to reduce low-frequency energy noise. Other deficiencies include the difficulty of mounting a tire to a wheel when using a conventional method, the possible damage if the conventional method fails during vehicle operation, and the inefficiency of conventional methods.
Conventional low-frequency noise absorbing methods exist. However, such conventional methods are not practical for small internal air chambers, such as a tire's air chamber. Such conventional low-frequency absorbing methods are too large for a tire air chamber, would prevent tire inflation, are not efficient, and/or pose safety hazards if used in combination with a tire.
Accordingly, a need exists in the art for reducing noise generated by or within tires and the wheels upon which the tires are mounted. Particularly, a need exists in the art for reducing tire noise by absorbing or reducing energy in the internal air chamber of a tire. More particularly, a need exists for a tire noise absorber/reducer that can absorb or reduce low frequency energy while operating inside a small internal air chamber, such as a tire's air chamber.